I assume here that you want to raise the elements of a matrix to a power (and not a matrix to a power) since you are using the ## operator. In general r to the a power will be multi-valued and complex if r is non-negative and a is non-integer, so the question arises, how do you want to handle complex values, and how do you want to choose a particular answer? It might be helpful to look at how these numbers arise and how you are using them?